# Do all flames require the same minimum concentration of oxygen to sustain themsleves?

Assume you have burned some substance A in an airtight container until the fire goes out due to insufficient oxygen. You then place some burning substance B in the container through an airlock. Are there substances A and B such that the substance B would continue to burn for a significant amount of time using the oxygen left behind after substance A burned out?

In other words, do all materials require the same concentration of oxygen to sustain a flame?

• Sep 2, 2018 at 10:35

You can understand this conceptually when you consider where the heat goes. On combustion in air some of the heat must be used to heat the $\pu{79\!\%}$ of the air that isn't oxygen and that heat is wasted in the inert gas and the heat is diluted. That means only ~$\pu{20\!\%}$ of the heat goes into activation energy to propogate the combustion. When the oxygen is more concentrated, less heat goes into inert gases and more goes into oxygen to propagate the combustion and vise-versa.